But you knew that. Microsoft has not tried to make all its products version agnostic.
See if the versions you have can save in some older version (97?) for compatibility.
I am running a gateway 800 select with win 98 and MS office 2000 Professional at home. I have a gateway select running Win XP with office 2003 Professional. Why can't I open files created with publisher (office 2000) with publisher (office 2003)?